Rotary-piston engine having temperature-corrected sealing arrangement



Sept. 3, 1963 ROTARY-PISTON Filed Jan. 18, 1962 INVENTOR. WALTER FRDEDE PRIOR ART @EENT Sept. 3, 1963 ROEDE 3,102,519

W. F ROTARY-PISTON ENGINE HAVING TEMPERATURE-CORRECTED Filed Jan. 18, 1962 SEALING ARRANGEMENT 3 Sheets-Sheet 2 INVENTOR. WALTER FRDEDE BYRW 7? WM AEENT Sept. 3, 1963 w. FROEDE 3,102,519

ROTARY-PISTON ENGINE HAVING TEMPERATURE-CORRECTED SEALING ARRANGEMENT C5 Sheets-Sheet 3 Filed Jan. 18, 1962 INVENTOR. WALTER FRDEDE AGENT United States Patent 3,102,519 ROTARY-PISTON ENGINE HAVING TEMPERA- TUBE-CORRECTED SEALING ARRANGEMENT Walter Froede, Necirarsulm, Wurttemberg, Germany, as-

srgnor to NSU Motorcnwerke Aktiengesellschaft, Neckarsuhn, and Wankel G.m.h.H., Lindau (Bodensee), Germany, corporations Filed Jan. 18, 1962, Ser. No. 167,077 Claims priority, application Germany Feb. 4, 1961 6 Claims. (Cl. 123-45) This invention relates to rotary piston combustion engines, and more particularly to such an engine having a sealing arrangement compensated for distortions arising from high temperatures.

As known in the prior art, rotary piston engines have a middle peripheral housing having a longitudinal axis, the housing being multicurved in cross-section transverse to the axis, preferably in a form that is basically epitrochoidal. The middle housing is closed by a pair of end plates having parallel inner surfaces, and there is positioned within the housing and between the end plates 21 multi-apexed rotor or rotary piston which is rotatable on an axis parallel to, but displaced from, the housing axis, while the rotor axis describes a planetary motion about the housing axis. Each apex of the rotor is provided with a longitudinally disposed radially movable sealing strip that sweeps along the multicurved inner surface of the middle housing in sealing relation thereto.

In engines of this type it may occur that the inner surface of the middle housing becomes deformed by heat at operating temperature, in such a way that the center portion of the housing, viewed in longitudinal section, bows slightly inward, somewhat in the manner of an hourglass. Because of this deformation, sealing strips having straight longitudinal contacting edges bear only at the center portion of the housing, which results in leakages. An even more serious matter is that with such a deformation and with seals bearing only in the center, they are able to make tilting motions about the contacting portion. Such tilting motions, because they take place under considerable gas pressures, are capable of causing the sealing strips to dig into the inner surface of the housing and of producing chatter marks, which in their turn may cause increased disorientation of the sealing strips.

These disadvantages are avoided by the present invention by forming the inner surface of the middle housing, as viewed in longitudinal section, with a concave outwardly curved form, and by appropriate contouring of the sealing strips. The inner surface may be given such a degree of curvature that at operating temperature it becomes substantially straight. Preferably, however, it should still retain some degree of outward concavity, which assures bearing of the sealing strips at their ends, thus avoiding pivoting movements. The slight leakiness which might then occur in the middle region can be avoided by likewise giving the contacting edges of the sealing strips an outward or convex curvature at the center. For the purpose of maintaining the bearing of the sealing strips at both ends, the radius of curvature from end to end of the contacting edge of the sealing strip is made greater than the radius of curvature of the inner surface of the housing from end to end; that is, the seal Will have less curvature than the housing.

In the present type of rotary combustion engine the individual phases of the operative cycle always occur at the same place in the housing. For this reason, the region of the housingin which combustion takes place is substantially hotter than the region in which induction occurs. Consequently, the amount of deformation of the inner housing surface varies from point to point. Therefore, for the purpose of achieving the objective of the ice invention, it is not necessary that the inner surface be outwardly concave to the same degree over its entire extent. This curvature can be made less in the cool region of the housing than in the hot region, or if desired may be omitted altogether in the cool region. Any leakiness that may occur in the cool region is of less importance than elsewhere because it does not result in a loss of fresh gas.

It is therefore an object of this invention to provide a rotary piston engine having '8. temperature-corrected sealing arrangement.

it is a further'object to provide a rotary piston engine having a housing with a temperature-corrected curvature.

Another object of the invention is to provide a rotary piston engine having temperature-correction against chattering of the seals.

The foregoing objects and others ancillary thereto will be readily understood on reading the following specification in connection with the drawings, in which- FIGURE 1 is a partial longitudinal cross-section of a rotary piston engine of the prior art;

FIGURE 2 is a cross-section similar to F-IGURE 1 of a rotary piston engine made in accordance with the invention;

FJGURE 3 is an end view of a sealing strip according to the invention;

FIGURE 4 is a fragmentary side view of a sealing strip;

FIGUPJE, 5 is a fragmentary plan view of the sealing edge of a sealing strip; and

BIGURE 6 is a schematic transverse cross-section of a rotary piston engine, with an apposed heat distribution curve.

In FIGURE 1 there is shown a middle housing 4 closed by two end plates 2 and 3, spaced apart by the middle housing and parallel with one another. The inner surface 5 of housing 4 is in transverse cross-section of multicurved form, preferably basically in the form of a multilobed epi-trochoid (better shown in FIGURE 6). Side plates 2 and B journal a crank 6 coaxial with the housing and having an eccentric 7 upon which a multiapexed rotor 8 is rotatably mounted. When a two-lobed epitrochoid, or basically epitrochoidal curve, is used for the inner contour of housing 4 the rotor is of generally triangular form with slightly convex sides, and at. each apex it bears a radially movable sealing strip 9 disposed longitudinally of the rotor and having a protruding edge 10 adapted to sweep along the inner surfaces in sealing relation thereto.

When inner surface 5 is formed parallel with the axis (as viewed in longitudinal section) in the cold state of the engine, the normal operating temperature will deform it as shown in FIGURE 1; that is, it will bow inward somewhat in hourglass fashion to form a constriction of the chamber. This has the result that sealing strip 9 bears by its straight contacting edge 10- only on the center of the inner surface, so that in the region of the ends of the sealing strip there are formed gaps '11, allowing gas leakage. Further, the hot gases flowing at high'speed through gaps 11 are capable of burning or eroding the sealing strip. An even more serious detriment is that the sealing strip is able to make a rocking motion about the center, as indicated by the arrows, which leads to damage of inner surface 5.

This drawback is remedied by the present invention as shown in FIGURE 2. As seen in longitudinal section,

- the inner surface 5 of the middle housing 4 is given a hollow-ground or outwardly curved concave form. This insures that the sealing strip 9 will hear at both ends against the inner contour, so that rocking motion is avoided. For the purpose of diminishing leakage that may occur in the middle portion during start-up and before the engine has reached normal operating temperature, the contacting edge 10 of the sealing strip is also arched outwardly; however, to be sure that the strip contacts at its ends, the radius of longitudinal curvature of the edge 10 is made greater than the radius of longitudinal curvature of the arched inner surface engine reaches operational heat the arch of the housing will flatten out slightly until the two curves substantially match.

With engines having the inner surface of the middle housing curved in the form of a multilobed epitrochoid as viewed in transverse 'cross-s'ection, during rotation of the rotor the sealing strips make, relative to the inner surface, a reciprocating tilting motion about a perpendicular to the path. The angle included between the longitudinal middle plane of the sealing strip and the perpendicular to the path is designated as the angle of tilt go. It is Zero when the sealing strip is situated at places where the inner surface of the middle housing is at its maximum and its minimum distance from the geometrical center of the inner contour. Between those points, the angle of tilt (p reaches its maximum value. The maximum angle of tilt depends on the shape of the epitrochoid, and is found from the formula:

l the sealing strip results, in practice a curve outside and parallel to the true epitrochoid is utilized. In this case the contacting edge of the sealing strip may be rounded off from side to side, to sweep a curved edge along the inner surface. The radius to which the edge is rounded As the,

the seal. Area F can also be seen in FIGURE 4, a side view of the sealing strip, and in FIGURE 5, a plan view of the edge. The curved borderline V of this area represents the line of contact at the maximum angle of tilt go. The sealing strip from its center to its ends may be beveled off below the line V to a non-interfering configuration, as shown.

If the thickness B of the sealing strip be given, there may be obtained from the foregoing equation the rise H of the longitudinal arc of the sealing strip, or the required depth of hollow grinding of inner surface 5:

FIGURE 6 shows schematically in transverse crosssection a rotary piston engine having an inner surface 5' paralleling a two-lobed epitrochoid. Lobe 24, refelred to as the coo lobe, is provided with an intake channel 12 for fuel-air mixture. The position of the ignition means is designated by the numeral 13. referred to as the hot lobe, there is provided an exhaust channel 15 for burned gases. Surrounding the epitrochoidal curve is a temperature distribution curve 16, its positioning from the epitrochoidal curve being determined by the length of the radiating lines 20 indicating heat transfer.

As will be seen from the heat distribution curve, lobe 14 is substantially hotter in operation than lobe 24, and consequently there occurs in the hot lobe a greater longitudinal deformation of inner surface 5 than in the cool corresponds to the spacing of the parallel curve from the true epitrochoid with which it is associated,

In accordance with the invention this relationship is utilized for the purpose of obtaining bearing of the sealing strip against the inner surface 5' throughout its longitudinal arc. Inner surface 5 being arcuate in a longitudinaldirection, it is composed of a family of curves all parallel to the same true epitrochoid, but spaced outwardly from the epitrochoid further at the center than at the ends. Therefore, the contacting edge of the sealing strip has a larger side-to-side rounding-01f radius at the center than at the ends. Because of this, when the inner surface is deformed by heat and its longitudinal arc flattens, the strip Will fit perfectly thereagainst with the proper edge-rounding at all points.

In FIGURE 3, T indicates the radial positioning of a true epitrochoid. The inner surface 5' has at its ends a spacing a outward from T, and at the center of its longitudinal are a spacing A outward from T. The rise of the longitudinal are of the sealing strip is therefore H=Aa. From this is obtained the relationship between this form of the inner surface 5 and the desired rounding of the sealing strip edge as follows. Since the line of contact at the center of inner surface 5' is to travel across the entire thickness B of the sealing strip, then:

B=sin a -2A The range over which the contact line travels at the ends of the seal, analogously, comes to:

Therefore the total range of the sealing strip edge over which the line of contact travels corresponds to area F of FIGURE 3, considering that figure as an end view of lobe. It is therefore not necessary for the inner surface "5 to be hollowground to the same depth over its entire changes and modifications may be made by those skilled in the art without departing from the invention. It is intended to cover all such modifications in the appended claims.

'What is claimed is:

l. A rotary piston engine having a multilobed peripheralhousing with an inner surface of basically epitrochoidal outline and having a longitudinal axis and having a fuel-intake port in one lobeof said housing and an exhaust port in another lobe of said housing, a multi-apexed rotor disposed within said housing and rotatable therein eccentrically about said axis, said rotor hearing at each apex a longitudinally disposed sealing strip having one edge in sealing relation to said inner surface and adapted to sweep said epitrochoidal outline, said inner surface being arcuately concave in the longitudinal direction.

2.- The combination recited in claim 1, wherein the sealing edges of said strips are arcuately convex in the longitudinal direction.

3. The combination recited in claim 2, wherein the outline of said inner surface is outside of and generally parallel to a true epitrochoid, and the sealing edges of said strips are arcuately convex in a direction transverse to the longitudinal axis.

4. The combination recited in claim 3, wherein the radius of transverse curvature of said sealing edges is greater at the middle of said edges than at the ends thereof.

5. The combination recited in claim 2, wherein the radius of longitudinal curvature of said sealing strip a greater degree of longitudinal concavity than the lobe having the intake port.

No references cited.

In lobe 14, 

1. A ROTARY PISTON ENGINE HAVING A MULTILOBED PERIPHERAL HOUSING WITH AN INNER SURFACE OF BASICALLY EPITROCHOIDAL OUTLINE AND HAVING A LONGITUDINAL AXIS AND HAVING A FUEL-INTAKE PORT IN ONE LOBE OF SAID HOUSING AND AN EXHAUST PORT IN ANOTHER LOBE OF SAID HOUSING, A MULTI-APEXED ROTOR DISPOSED WITHIN SAID HOUSING AND ROTATABLE THEREIN ECCENTRICALLY ABOUT SAID AXIS, SAID ROTOR BEARING AT EACH APEX A LONGITUDINALLY DISPOSED SEALING STRIP HAVING ONE EDGE IN SEALING RELATION TO SAID INNER SURFACE AND ADAPTED TO SWEEP SAID EPITROCHOIDAL OUTLINE, SAID INNER SURFACE BEING ARCUATELY CONCAVE IN THE LONGITUDINAL DIRECTION. 